In order to cope with the challenges caused by the pollution of internal combustion engines and the shortage of petroleum resources, many new engines with low energy consumption and low pollution characteristics have been developed, including electric motors, fuel cell engines, aerodynamic engines, and hybrids. Engines, etc., in which compressed air/fuel hybrid engines have become one of the research hotspots. In this paper, I propose a new concept of compressed air/fuel hybrid engine that can operate in both compressed air power mode and internal combustion engine mode. Vehicles equipped with this hybrid engine are more suitable for cities. traffic. In the start-up and low-speed phases, the compressed air is used as the power source to operate the engine in the compressed air power mode, which can be used to produce low-speed, high-torque and zero-pollution emissions of the compressed air-powered engine. The use of the internal combustion engine mode at a higher speed or load can avoid the disadvantages of high energy consumption and harmful emissions at low speeds of the internal combustion engine, so that the engine operates in the vicinity of the optimal operating conditions of low energy consumption and low pollution.
1. Gas storage tank 2. Pressure reducing valve 3. Heat exchanger 4. Flow valve 5. Electromagnetic switching valve 6. Compressed air nozzle 7. Intake valve 8. Injector 9. Electronically controlled fuel injection device 10. Exhaust Door 11. Cylinder 12. Piston 13. Schematic diagram of single-cylinder hybrid engine with crank-link mechanism. Based on the numerical simulation of the first law of thermodynamics in the working process of compressed air/fuel hybrid engine, the second law of thermodynamics is applied. Work Process Fund Projects of Two Working Models: National Natural Science Fund-Ford Fund-funded Project (50122115) (the middle dashed line enveloping part) is assumed to simplify the calculation: 1 The gas state in the cylinder is uniform, the pressure and temperature at each point in the cylinder The same is true; 2 working fluid is ideal gas specific heat, internal energy, helium and other parameters are only related to gas temperature and gas composition; 3 gas into or out of the cylinder is quasi-stable flow; 4 kinetic energy of the inlet and outlet gas is negligible.
1.1 Compressed aerodynamic mode The energy balance mode can be used to compress the aerodynamic mode. The working process of the engine is the process of changing the thermodynamic state of the gas. The first law of thermodynamics can be used to obtain the energy conservation equation of the system: the bound heat exchange; hi, hE, he are the intake, exhaust and compressed air intake ratio ç„“; mi, mE, m (: intake, Exhaust and compressed air intake quality; 9 is the crank angle. T is the in-cylinder working temperature.
The instantaneous mass of gas entering and exiting the cylinder is a one-dimensional isentropic adiabatic flow, and the rate of change with the crank angle is the opening area; pi is the gas pressure before the inlet and outlet; P is the instantaneous density of the gas before and after the inlet and outlet; Flow function.
The available energy balance equation of the system in compressed aerodynamic mode can be obtained by the second law of thermodynamics: flow: Aw, available energy for piston work; Aq is available energy for cylinder wall heat transfer; A is available energy in the system; Ad is irreversible Loss of available energy.
The available energy per unit mass of compressed air in the gas tank is calculated by the following equation: The amount of heat exchange between the system and the cylinder wall can be written as: pressure.
(2) The available energy change of the intake air into the system is the average temperature of the heat transfer surface.
1.2 The internal combustion engine mode can use the energy balance equation to be similar to the compressed aerodynamic mode. The first law of thermodynamics can obtain the energy conservation equation of the system under the internal combustion engine mode: (4) the change of available energy of the piston work is (7) the available energy change caused by fuel combustion. The amount is determined by: (5) The amount of energy available for heat transfer from the system to the cylinder wall is the specific entropy.
(3) The amount of available energy removed from the system is obtained by the second law of thermodynamics. The available energy balance equation for the system in internal combustion engine mode: cylinder diameter (mm) 62 piston stroke (mm) 66 compression ratio 8.7 suction pressure (MPa) 0.10 exhaust pressure (MPa) 0.11 compressed air intake pressure (MPa) 3.00 ambient pressure (MPa) 0.10 ambient temperature (IO 293 material burning percentage.
The fuel heat release rate dX/d can be simulated by Weibo on the exothermic curve, and the calculation accuracy is sufficient. The empirical formula is as follows: the initial angle.
The calculation of other available energy change terms in the energy balance equation for the internal combustion engine mode can be found in the compressed aerodynamic mode.
2 Working process available energy analysis Based on the above mathematical model, based on the application of the first law of thermodynamics numerical simulation to obtain the instantaneous temperature, pressure and gas quality in the cylinder, the second law of thermodynamics is applied to the working process of the two working modes of the hybrid engine. Energy availability analysis calculations. In urban traffic, the average speed is usually around 40km/h, and the engine speed is generally between 1500~1800r/min. In the simulation calculation, the switching speeds of the two working modes are set to 1500r/min. The initial parameters of other simulation calculations are shown in Table 1. Table 1 Hybrid engine simulation initial parameters 2.1 Compressed aerodynamic mode available energy analysis 180°) as the starting point of calculation, at 355 ° (ie, when the compressed air intake advance angle is 5°, open the electromagnetic switch valve to inject compressed air into the cylinder, and close the electromagnetic on-off valve at =445° (ie, the compressed air intake angle is 90°). The curve (,) of the available energy of the system with the crank angle can be obtained when the speed is 1500r/min.
Shown is the curve of the available energy in the cylinder during the valve closing period as a function of the crank angle. Since the pressure difference between the compressed air intake pressure and the in-cylinder pressure is large, as the electromagnetic on-off valve is opened, the available air entering the cylinder can be rapidly increased. When the compression stroke is performed, the piston works on the system, and the available energy in the system increases. As the compressed air is injected into the cylinder, it gradually increases to the peak value, and then gradually decreases with the expansion stroke. The piston work is negative when the stroke is compressed, and the piston work increases to a positive value during the expansion stroke, and gradually increases as the gas in the cylinder expands. During the valve closing period, the heat transfer energy can be gradually increased from a negative value to a positive value, which indicates that the gas in the cylinder absorbs heat from the environment, but the heat transfer energy is small. The irreversibility is approximately zero during the compression stroke and gradually increases during the compressed air intake and expansion strokes.
3. Irreversible process available energy loss 4. Piston work available energy 5. Cylinder wall heat transfer Available energy Compressible aerodynamic mode Instantly available energy (valve closing period) is shown as the available energy change curve in the valve opening period. The piston work is slightly reduced with the exhaust stroke and increases slightly with the intake stroke. The available energy of the exhaust gas gradually increases and peaks with the exhaust stroke. The available energy in the system can be quickly reduced after the exhaust valve is opened, and gradually decreases as the exhaust gas is negative. This is because the in-cylinder temperature is lower than the ambient temperature and has a certain amount of cooling. The ambient air enters during the intake stroke. In the cylinder, the temperature inside the cylinder rises and the available energy in the system increases slightly. The available energy loss due to the irreversible process increases slightly during the exhaust process and decreases slightly during the intake process.
Table 2 shows the available energy distribution of a work cycle for a compressed aerodynamic mode engine. The available energy obtained by the system through the heat exchange of the cylinder wall is small, and the loss of available energy is mainly caused by the decompression loss of the compressed air, the loss of available energy of the exhaust gas and the irreversibility. Only 64 2% of the compressed air available per cycle can be utilized, which means that the available energy loss caused by throttling decompression accounts for 358%. To improve the available energy utilization of compressed air, try to reduce the available energy loss during the decompression process. An important aspect. Studies have shown that reducing the pressure difference before and after throttling and using the volume decompression mode 101 can greatly reduce the energy loss of throttling. The available energy loss caused by the exhaust gas accounts for about 19.3% of the available energy of the compressed air, and the exhaust gas is a cold air with a certain pressure, which can be recycled, for example, can be used as a cold air source for the air conditioner of the vehicle. Thereby improving the energy utilization of the engine.
Available energy categories ATAcaQAwAeAd available energy available energy class afAWaqaiAEAD available energy table 2 compressed aerodynamic mode each work cycle available energy distribution 2.2 internal combustion engine mode available energy analysis, shown in the internal combustion engine mode speed 1500r / min, excess air When the coefficient is 1 1, the available energy in the cylinder changes with the crank angle. As shown, the available energy, the available energy of the piston, the available energy of the system, and the irreversibility of the fuel combustion during the valve closing period are basically the same as those of the compressed aerodynamic mode. The available heat transfer between the cylinder wall and the pressure aerodynamic mode is different because the temperature inside the system is much higher than the temperature of the cylinder wall. The system radiates heat to the environment through the cylinder wall, and the heat release is much larger than the heat absorption in the compressed air power mode. .
5. Cylinder wall heat transfer can be used in the internal combustion engine mode instantaneous available energy (valve closing period). As shown, the available energy of the exhaust valve during the valve opening period and the available energy of the piston work are also similar to the compressed aerodynamic mode. The available energy in the system drops rapidly after the exhaust valve is opened, and is close to zero before the exhaust ends, and is basically unchanged during the intake process, which is approximately zero. The available energy of the cylinder wall heat transfer changes little, and the irreversibility increases slightly during the valve opening period.
3. Exhaust available energy 4. Available energy in the system 5. Cylinder wall heat transfer Available energy engine mode Instantly available energy (valve opening period) Table 3 shows the available energy distribution of the engine in the internal combustion engine mode. The loss of available energy is mainly due to cylinder wall heat transfer, exhaust process and irreversibility. Among them, the available energy loss of exhaust gas reaches about 20% of the available energy of fuel combustion. The exhaust energy available recovery measures can significantly improve the energy utilization of the engine. The currently used engine boost technology utilizes the available energy of the exhaust.
The internal combustion engine mode can be distributed for each work cycle. 3 Conclusion Compressed air decompression loss and exhaust energy available energy account for 358% and 19.3% of the available energy of compressed air, respectively. Therefore, how to reduce the decompression loss and use the exhaust energy can improve compression. The key to aerodynamic mode efficiency.
In the internal combustion engine mode, the available energy loss of exhaust gas accounts for 202% of the energy available for fuel combustion, so the full utilization of the available energy of the exhaust gas can significantly improve the efficiency of the internal combustion engine mode.
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